CAVSIM is a three-dimensional, axisymmetric model for resource recovery and cavity growth during underground coal gasification (UCG). CAVSIM is capable of following the evolution of the cavity from near startup to exhaustion, and couples explicitly wall and roof surface growth to material and energy balances in the underlying rubble zones. Growth mechanisms are allowed to change smoothly as the system evolves from a small, relatively empty cavity low in the coal seam to a large, almost completely rubble-filled cavity extending high into the overburden rock. The model is applicable to nonswelling coals of arbitrary seam thickness and can handle a variety of gas injection flow schedules or compositions. Water influx from the coal aquifer is calculated by a gravity drainage-permeation submodel which is integrated into the general solution. The cavity is considered to consist of up to three distinct rubble zones and a void space at the top. Resistance to gas flow injected from a stationary source at the cavity floor is assumed to be concentrated in the ash pile, which builds up around the source, and also the overburden rubble which accumulates on top of this ash once overburden rock is exposed at the cavity top. Char rubble zones at the cavity side and edges are assumed to be highly permeable. Flow of injected gas through the ash to char rubble piles and the void space is coupled by material and energy balances to cavity growth at the rubble/coal, void/coal and void/rock interfaces. One preprocessor and two postprocessor programs are included - SPALL calculates one-dimensional mean spalling rates of coal or rock surfaces exposed to high temperatures and generates CAVSIM input: TAB reads CAVSIM binary output files and generates ASCII tables of selected data for display; and PLOT produces dot matrix printer or HP printer plots from TAB output.

The gas flow distribution is obtained by solving the compressible Darcy flow equation written in cylindrical (r,z) coordinates using a finite difference algorithm. The injection flow distribution to the wall and outer and inner bed regions is calculated for a given ash pile geometry, and bulk densities for the ash, char, and rock rubble are specified. The system of nonlinear equations for a fixed fraction of spalled char are solved simultaneously by Newton iteration to determine the temperatures of all surfaces enclosing the void. Wall recession rates and char and ash addition rates from the wall model, and char and ash addition rates from the inner and outer bed regions are calculated. Once a solution is obtained for the char fraction, a tentative time-step is taken, cavity boudnaries are advanced, and new ash and char amounts are calculated. The char fraction is adjusted using a golden section scheme, and the process is repeated until both ash and char mass balances are satisfied and a solution for the new cavity shape obtained.

COMPUTER

IBM PC

OPERATING SYSTEMS

DOS 3.2.

SOFTWARE LIMITATIONS

CAVSIM does not work with MS FORTRAN 4.0x. CAVSIM uses the LSODE (NESC) 592) ordinary differential equation solver, which is included. PLOT uses DIGLIB/PC (NESC 9639); this software is not included.

OTHER PROG/OPER SYS INFO

CAVSIM does not work with MS FORTRAN 4.0x. CAVSIM uses the LSODE (NESC 592) ordinary differential equation solver, which is included. PLOT uses DIGLIB/PC (NESC 9639); this software is not included.